The present invention relates to adhesive compositions which are particularly useful for adhesion on moist or wet surfaces, where they provide an increased adhesion capability and stability. Particularly, the adhesive compositions of the present invention are suitable as topical adhesives for attachment to the skin, for example in absorbent articles for absorption of body fluids, such as to attach sanitary napkins or pantiliners in the genital region. Also incontinence devices which are worn e.g. in the genital region or perspiration pads which are worn in the arm pit region of a person can suitably employ the adhesive compositions of the present invention in order to be directly adhered to the wearer's skin.
Adhesive compositions for attachment to the skin have been generally disclosed in for example US statutory invention registration H1602 or WO 96/33683 and WO 95/16424. The latter discloses sanitary articles having a topical adhesive which is applied on the wearer facing side of a sanitary napkin along the entire periphery. WO 96/13238 discloses a topical adhesive which is described in terms of frequency dependency. EP 638303 discloses the use of a topical adhesive on side cuffs of sanitary napkins in order to keep the cuffs in an upright position. Swiss publication CH 643730 discloses the use of a very long sanitary napkin having chamfered outer edges with a topical adhesive at the four corners of the outer edges in order to provide a topical adhesive area well outside the region of pubic hair growth.
However all of these disclosures typically disclose a product which is designed to be utilised in combination with an undergarment and hence the degree of adhesion actually provided is very low and is not designed to withstand any excessive stress or force. Moreover the adhesive is only discussed in general terms or concentrates on the area of application of the adhesive to the article. The nature of adhesive per se other than the basic physical requirements such as pressure sensitivity are not discussed in particular with reference to the chemical composition or the adhesive criteria.
The prior art in the general field of adhesives for attachment to the skin is particularly developed in the field of articles such as band-aids, plasters and bandages. These articles are however typically applied in an emergency situation, where for example, a cut into the skin of the wearer has occurred. In this context, performance aspects of the article such as easy application and use of the product, comfortable wear as well as painless removal, and discreteness are subordinate to other criteria such as sterility, healing support, and mechanical protection of the wound. Also such wound covering absorbent articles are mostly adhered to the skin where prior to application of the absorbent article bodily hair can be removed or where little hair grows.
In order to provide in all possible situations the desired level of adhesion of such bandages, the prior art typically discloses the utilisation of certain adhesives having very high adhesive and cohesive strengths such as rubber based adhesives, comprising natural rubber or synthetic rubbers, and acrylics. In order to achieve the desired level of adhesive force upon application, and also an acceptable adhesion stability in presence of moist or wet skin, these adhesives are formulated so as to provide a very high level of initial adhesion, and are also very hard, i.e., in rheological terms, have a high elastic modulus G′. This implies these adhesives are not comfortable and skin friendly, but rather aggressive, and cause a substantial level of pain upon removal.
On the contrary, for application on the skin, and in particular for application in absorbent articles to be directly adhered to the wearer's skin, it is important that the adhesive has a skin compatible composition and is not harsh or aggressive towards the skin or cause skin irritation or inflammation. Also it is preferred if the adhesive is compliant with the skin of the wearer such that maximum skin surface contact between the adhesive and the skin is achieved. In this way a sufficient level of adhesion can be achieved even with adhesives having a non aggressive adhesive strength. Moreover, it is also desirable to provide an adhesive such that the absorbent article can be readily removed from the wearer, without the wearer experiencing any unacceptable pain level. This is particularly important under circumstances, where the article is removed and reapplication of the article once or even a number of times is required, for example to allow for urination and/or to ensure the application of such articles on sensitive skin and wearer groups such as infants. However, on the other hand the desired level of adhesion, albeit painless should of course also be maintained during such multiple applications of the article.
The problem of achieving the desired adhesion level is further exacerbated under wet skin conditions. Typically, during the placement of the article the skin has a physiological level of moistness which varies among individuals, and can also by very high.
The currently available adhesives often do not immediately strongly adhere to wet skin and may need to be held in place until sufficient minimum adhesion occurs. Moreover, the overall adhesive ability of such adhesives tends to be significantly reduced on wet skin surfaces per se, so that the article will typically not remain attached to the skin during wear if any force or stress is exerted onto the article, for example by the movement of the wearer.
Moist and wet skin however is not just a problem which is prevalent at the article application stage as a significant amount of moisture is also generated during the use of the article by the wearer by perspiration and from bodily fluids, which can also come in contact, even in large amounts, with the adhesive. With currently available adhesives the adhesive strength is reduced under such circumstances to such an extent that the article will often become detached spontaneously or under exertion of even minimal force or stress during wear.
More in general, effective adhesion capability and adhesion stability on wet or moist surfaces, either at the application stage, or with respect to moisture or liquid getting in contact with the adhesive during its use, are desirable in adhesive composition also for different uses besides the preferred application in articles, typically absorbent articles, intended to be kept in contact with the skin.
Among the adhesives known in the art as topical adhesives for attachment to dry and wet skin there are adhesives of the hydrocolloid type typically comprising a hydrophobic polymeric matrix, e.g. constituted by a synthetic rubber, preferably polyisobutylene, in which water soluble or water swellable hydrocolloids, such as for example particles of pectin, gelatin, or carboxymethylcellulose, are dispersed. In adhesive compositions of this type, the hydrophobic polymeric matrix provides the adhesive properties in dry conditions, while the dispersed hydrocolloid particles absorb aqueous fluids and render the adhesive at least to a certain extent, capable of adhering to moist surfaces, typically moist skin. Absorption is however not very efficient, since the hydrocolloid particles are surrounded by and often enclosed into a hydrophobic matrix.
An increase of the hydrocolloid content in order to enhance the liquid absorption capacity and to facilitate the access of liquids to the absorbent particles, on the other hand, can also cause the hydrocolloid adhesives to break down upon exposure to relatively large amounts of fluids, for example when they are employed for attachment to the skin of articles intended for absorption of body fluids, e.g. incontinence devices, where they typically also act as skin barriers, i.e. providing a seal against liquid leakage. Upon contact with relatively large amounts of fluids, in fact, the swelling of the hydrocolloid particles may cause the adhesive composition to lose its integrity. This results in a loss of the barrier effect, and also, very often, in residues remaining on the skin upon removal of the article. In addition, hydrocolloid adhesives are typically rather hard and not very pleasant to the skin, and may also cause pain upon removal. This is due to the particular structure of the hydrocolloid adhesives, in which the inclusion of a hydrocolloid incompatible disperse phase into a hydrophobic rubbery continuous matrix causes the resulting material to be harder, i.e., in rheological terms, having higher elastic modulus G′ and storage modulus G″, which, in turn, render the initial adhesion to the skin more difficult, and the removal painful.
Other known adhesive compositions that are particularly useful as topical adhesives for attachment to the skin are those having a substantially gel-like structure, and are preferably gels. They typically comprise as a prevailing component a plasticiser which is a material liquid at room temperature, and a macromolecular or polymeric component forming, in the preferred embodiments, a three dimensional network caused by physical or chemical links between the molecules. Such adhesive compositions can be classified according to the nature of the main component, i.e. usually the plasticiser. Hydrophobic compositions, also known as oil-gels, are those in which the plasticiser is typically an oil or blend of oils of vegetable or mineral origin and the polymer is usually a synthetic hydrophobic polymer, preferably an elastomer, soluble or swellable in oil(s). Hydrophilic compositions, also known as hydrogels, are those in which typically the plasticiser is water/glycerol/glycols and the like and/or mixtures thereof, and the polymeric phase is of synthetic (e.g. polyacrylics) or natural (e.g. natural gums) origin. Mixed phase compositions are also known, in which both hydrophobic and hydrophilic components, possibly in both plasticisers and polymers, form two or more separate phases.
The gel and gel-like adhesive compositions can be suitably formulated in order to have rheological and physical characteristics which render them soft and pleasant to the skin, provide firm adhesion also on skin surface with hairs, with low pain level upon removal. However, they can still be improved in their adhesion characteristics on moist or wet surfaces, typically moist or wet skin, and particularly also in the presence of a significant amount of moisture or liquid generated during the use of the adhesive, i.e. during the time the adhesive is actually adhered to the surface, e.g. the skin.
The above mentioned oil-gel type adhesives are in fact not capable of absorbing moisture or aqueous liquid due to their chemical nature, and therefore their adhesion on moist or wet surfaces is limited if none at all. Once they are adhered to a surface, e.g. the skin, they cannot withstand the presence or the build up (e.g. by sweating) of even relatively small amounts of moisture or liquid generated during the use, and loose, their adhesion capacity to a substantial extent, to the point they can spontaneously detach from the surface.
Hydrogel type adhesives on the other hand have typically a very high liquid absorption capacity, and while they are effective in presence of limited amounts of moisture or liquid on the surface when they are adhered, or generated during the use, since they can absorb such limited amounts of moisture or aqueous liquid still maintaining an acceptable level of adhesion onto the surface, their high absorption capacity can constitute a disadvantage in presence of substantial amounts of moisture or liquid: They in fact tend to absorb water to such an extent, that they dramatically change their rheology and loose their adhesion capability very quickly after contact with such high amounts of moisture or aqueous liquid.
Mixed phase adhesive compositions are typically harder than both oil-gels and hydrogels, and since they comprise a hydrophobic phase and a hydrophilic phase, they basically have the drawbacks of both oil-gels and hydrogels as described above. Moreover, if the hydrophilic phase is the disperse phase, they tend to behave like hydrocolloid adhesives upon absorption increasing the phase separation owing to the absorption into the disperse hydrophilic phase, with risk of loss of integrity as explained above.
Examples of gel or gel-like adhesives are disclosed in the prior art.
U.S. Pat. No. 4,699,146 discloses hydrophilic elastomeric pressure sensitive adhesives suitable for use with ostomy devices, bandages, ulcer pads, sanitary napkins, diapers, and athletic padding. The adhesive comprises at least an irradiation cross linked organic polymer and an adhesive plasticizer.
GB 2115431 discloses adhesives for bandages, wounds or burn dressings, EKG adhesives, sanitary napkins, diapers and ulcer pads. The adhesive comprises an irradiation cross linked organic polymer such as polyvinylpyrrolidone and an adhesive plasticizer.
Adhesion to wet skin is addressed for example in WO 98/03208 which discloses medical pressure sensitive adhesives which can adhere to dry or wet skin and which comprise a mixed phase composition comprising a mixture of hydrophilic (meth)acrylate copolymer containing tertiary amino groups, a hydrophobic (meth)acrylate copolymer containing carboxyl groups, carboxylic acids and a crosslinking system. However this document does not discuss adhesion after exposure to excess liquid.
Moreover gel-like adhesives, particularly hydrogels, need to be crosslinked in order to achieve their three dimensional network, and typically this crosslinking step occurs after application of the not crosslinked composition over a suitable substrate, hence implying a rather complex process for the formation of articles comprising said adhesives.
In addition hydrogel adhesives, owing to their capability to exchange water with the environment, lose or acquire it depending on the external conditions, and therefore can substantially change their rheology and hence their adhesive behaviour. As a consequence, hydrogel adhesives need to be stored in water- and moisture-proof packages.
Hence there still exists a need for an adhesive composition having an increased adhesion capability and stability on moist or wet surfaces, particularly on moist or wet skin, and more particularly in the presence of significant amounts of moisture or liquid, independently of whether this is upon direct application of the article to the moist or wet surface, e.g. skin, or when moisture or liquid is generated on the surface or in any case contacts the adhesive during its use. In particular it is an objective of the present invention to provide an adhesive which is liquid stable particularly to water and aqueous fluids and more particularly to body fluids such as menses, urine, or sweat in its use as topical adhesive for skin attachment, such that the adhesion properties will not be significantly affected by the presence of said fluids over the period of use of an article for the absorption of body fluids comprising the adhesive of the present invention.
It is another object of the present invention to provided an adhesive composition having the above characteristics and which is also particularly suitable in the use as a topical adhesive for skin attachment for the secure attachment and painless removal from the skin, particularly for use on sensitive skin of an infant and/or of the genitalia.
It is still another object of the present invention to provide an adhesive composition which is moisture vapour permeable, while also preferably being capable of providing a seal against liquid leakage, which is particularly desired in the preferred use as topical adhesive for attachment of articles to the skin, particularly disposable absorbent articles, where the adhesive can therefore act as skin barrier.
It is a further object of the present invention to provide an adhesive composition that also exhibits an ability to adhere to a surface, e.g. skin, upon reapplication, particularly multiple reapplication for example when an article, e.g. an absorbent article, comprising the adhesive is removed for urination purposes or is misplaced, whilst still allowing painless removal.
An additional object of the present invention is to provide an adhesive composition which provides flexibility, stretchability and contractability so that it is able to adapt to the contours of the surface where it has to be applied, and particularly of the body during all bodily movements hence be comfortable for the wearer of the article comprising the adhesive composition whilst still having sufficient adhesive capacity to ensure secure attachment during use.
It has now been surprisingly found that the above drawbacks of the known adhesives, typically employed as topical adhesive for attachment to the skin, can be substantially alleviated by providing the adhesive compositions defined hereinafter. The adhesive compositions have an increased adhesion capability and stability on moist or wet surfaces, particularly on moist or wet skin. In their preferred use as topical adhesives for skin they provide a secure attachment, and yet cause no discomfort upon removal and maintain their adhesive strength over the period of use even under exposure to excess liquids.
The adhesive compositions are also simple to produce and to incorporate into articles, namely by means of direct coating, e.g. by means of known hot melt coating techniques, onto a suitable substrate or directly onto the article. They are also substantially stable both in storage and during use, and do not necessitate a particular packaging.
All the above mentioned advantages are achieved by the adhesive composition of the present invention, which is provided by suitably formulating a thermoplastic polymeric matrix which is at the same time homogeneous and intrinsically hydrophilic, and preferably also moisture vapour permeable, as will be described hereinafter.